Over 40 million individuals in the U.S. suffer from any one of the following respiratory tract diseases or infections: chronic obstructive pulmonary disease (COPD), asthma, cystic fibrosis, or other respiratory afflictions. Worldwide, the most serious diseases continue to grow at alarming rates. The prevalence of asthma increased 75% between 1980 and 1995, and an estimated 10% of the population over 64 suffers from COPD. According to statistics from the World Health Organization, COPD is projected to be the 5th leading cause of disease by the year 2020. Americans spend over $6.0 billion/year for treatment of respiratory distress.
There are five main categories of treatment available for COPD:
1. Bronchodilators, such as albuterol, pirbuterol, isoetherine, metaproteranol, terbutaline, salmeterol.
2. Anti-Inflammatories (Steroids), such as prednisone, methylprednisolone.
3. Oxygen
4. Lung Reduction Surgery
5. Transplant Surgery
A number of pulmonary function tests (PFT's) are routinely carried out to evaluate the overall performance of lungs. These take from 1-3 hours depending on the tests. These tests include, for example, spirometry, sputum test, lung volume tests, diffusing capacity test, methacholine challenge tests (testing for asthma), allergen bronchial challenge tests (testing for specific allergies), airway resistance test (looking for obstruction in the large airways), and lung compliance test (measuring the elasticity of the lungs, which is reduced in emphysema). X-ray analysis is the diagnostic tool of choice for occupational diseases caused by work environment pollutants, such as, silica, coal, cement, asbestos, smoke, coal dust, etc.
Most of these tests, however, are useful only for evaluating lung capacity, and not lung function. Lung capacity and airway resistance measured by spirometry generally relates to a volume of gas expired by a particular set of lungs. Lung function, in contrast, is the capability of the lung to provide oxygen to the blood and remove carbon dioxide, i.e., the ability to perform alveolar gas exchange efficiently. Any lung obstruction caused by environmental pollutants can affect the extent of alveolar gas exchange, either by slowing down the inhalation of oxygen, the exhalation of carbon dioxide, or both. Lung function, thus, provides a more reliable diagnostic tool for obstructive respiratory problems than lung capacity, as it relates to the efficiency of the gas exchange process.
The only lung function assay available of any clinical significance is Arterial blood gas (ABG). The ABG test produces four main measurements: arterial pH, paO2, paCO2 and HCO3−. The arterial pH is a measure of the body's acid-base equilibrium. Any major alteration of the pH (normal levels 7.35-7.45) can prove fatal. The arterial paO2 indicates the oxygenation of the blood (normal levels 80-100 mmHg). A low paO2 can also prove fatal and appropriate oxygen therapy is usually given to correct a low paO2. The ability to excrete CO2 is one of the major respiratory functions of the lung, and the arterial paCO2 measures the ability of the body to excrete carbon dioxide (normal levels 35-45 mmHg). An elevated paCO2 may suggest a problem with lung ventilation that could progress to require mechanical ventilation. The importance of bicarbonate (HCO3−) lies in its role as the renal or metabolic component of acid-base regulation, with normal HCO3− levels being 22-28 mEq/L. ABG is, however, an invasive and painful test.
Accordingly, there remains a continuing need to develop an assay to determine lung function.